The perovskite oxide LaCoO$_{3}$ exhibits an anomaly in its magnetic
susceptibility at 80 K associated with a thermally excited
transition of the
Co$^{3+}$-ion spin. We will show that atomic-resolution
Z-contrast imaging
and electron energy-loss spectroscopy in combination with ab-initio
first-principles DFT calculations can be utilized to measure the
spin-state
transition in LaCoO$_{3}$. In particular, we utilize in-situ cooling
experiments in a transmission electron microscope to demonstrate
that the O
K-edge pre-peak is sensitive to the Co$^{3+}$-ion spin-state. Our
experimental results will be compared to first-principles
calculations, and
we will conclude that the thermally excited spin-state transition
occurs
from a low to an intermediate spin state, which can be
distinguished from
the high-spin state. Next, we will examine the effects of
bi-axial strain
and point defects in LaCoO$_{3}$ thin-films on the Co$^{3+}$-ion
spin-state.
We will show that a single-crystal pseudo-cubic LaCoO$_{3}$ (001)
film can
be successfully grown on LaAlO$_{3}$ (001). Moreover, we will
show that the
epitaxially strained LaCoO$_{3}$ film exhibits a ferro-magnetic
transition
at low temperature that was not observed in bulk LaCoO$_{3}$. We
will
discuss the origin of this transition and the possibility of
stabilizing
different Co$^{3+}$-ion spin-states in LaCoO$_{3}$ using
interfacial strain.

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2009.MAR.D30.7